Mr. W, Clark on the Littorinidse. 363 



rocks, when they will at once perceive that they are all identical 

 with each other and the type L. rudis, and will afford a practical 

 proof that species founded on the characters of the shells are ar- 

 tificial and delusive, and that the soft parts must also be consi- 

 dered to obtain specific distinction. 



The L. rudis, and all the varieties, are extremely impatient of 

 continued immersion in water ; when deposited in basins, the first 

 object is to escape therefrom and attach themselves to a dry spot. 

 In estuaries, where they are often affused by the fresh water, they 

 become, particularly the L. tenebrosa, thin and depauperated in 

 their shells ; they are sometimes for weeks deprived of even being 

 sprinkled by sea water. Though decided Pectinibranchiata, they 

 live in the open air with nearly equal facility as the Pulmonifera ; 

 and in reference to this fact, as regards another family, the Cono- 

 vuli, there are still malacologists, who, notwithstanding the va- 

 luable observations of the Rev. T. Lowe, are not quite satisfied 

 that they are pulmoniferous ; we have ourselves attempted to 

 corroborate Mr. Lowers views, but failed from want of sufficient 

 specimens. 



The L. littorea is the only species of this particular form that 

 requires, to attain full growth, a regular bi-hodiernal immersion 

 in sea water, and to obtain it the bulk of that species live in the 

 lower littoral levels ; if they are deprived of it, they become stunted 

 and dwarf. 



That variety of the L. rudis which is undoubtedly the L. ju- 

 gosa of Montagu varies from quite smooth to highly striated, 

 and has even ridged, reflected, spiral volutions, as are repre- 

 sented in the figure of Montagues ' Testacea Britannica -/ it 

 clothes the interstices of rocks on the Devon coasts in myriads ; 

 they are rarely or never immersed, as they dwell in the same 

 highest littoral levels, in most exposed situations, in like manner 

 as their congeners the L. rudis and L. tenebrosa inhabit the highest 

 levels of the sheltered and protected estuaries. They are the 

 parents of all the dwarf varieties, the L. patula, L. subsaxatilis, 

 L. neglecta and L. fabalis, &c. 



As a proof that habitat is the cause of these dwarf varieties of 

 the L. rudis, I mention that the L. littorea in company with 

 them, at a few yards' lower level, are small, stunted, and nearly as 

 dwarfish. By the favour of Mr. Bean of Scarborough I have 

 compared his L. zonaria, L. rudissima, L. neglecta o^ndiL. fabalis 

 with Devon specimens, and found them identical ; consequently 

 I presume the animals are so likewise. 



These so-called species are without exception viviparous. How 

 happens this singular coincidence ? how is it that none of them 

 follow the plan of the reproduction of the other species ? This is 

 a very significant fact, and is, I think, a strong circumstance, in 

 conjunction Vv ith the positive similarity of the animals, in favour 



